\"She is the worst secretary of state in history,\" Trump has said of Clinton.

But for the next generation of Trumps and Clintons, things are a little different.

Ivanka and Chelsea have developed a close, private friendship over the years -- a relationship that will likely be tested as their parents make their way through the primary season and into even hotter waters if they face off against each other in the general election.

The two women are both in their thirties -- Clinton, 35, and Trump, 33. They are both new moms and live in Manhattan.

But beyond surface level similarities, their connection likely goes deeper, steeped in the commonalities of their unconventional upbringings. Chelsea grew up in the most famous of houses, at 1600 Pennsylvania Avenue as the nation's first daughter; Ivanka grew up among New York's elite, the daughter of a powerful and wealthy real estate mogul.

Their career paths, although vastly different in direction, also have echoes of familiarity.

They each have a big role in their respective family businesses, though they each have also worked on their own separate projects and jobs over the years. Ivanka has appeared on NBC's \"The Apprentice\" and is also a top executive at the Trump Organization. Similarly, after a stint as a consultant at McKinsey & Co., Chelsea now has prominent role at the Clinton Foundation and Clinton Global Initiative.

But it may be their choice in a spouse that has linked the two most powerfully.

\"They have been out together, they have been on a double-date with their husbands,\" Emily Heil, co-author of The Washington Post's Reliable Source column said. \"There's so much that they understand about each other. If there's anyone who understands what Chelsea Clinton has been through it is Ivanka Trump.\"

Both women also married men of the Jewish faith, with Ivanka converting to Judaism.

On social media they both seem to be president of the other's fan club -- tweeting at each other and posting praise on Facebook.

Chelsea told \"Vogue\" magazine that there's nothing \"skin deep\" about Ivanka, that she is always aware of everyone else around her.

\"It's an awareness that in some ways reminds me of my Dad, and his ability to increase the joy of the room,\" Chelsea said.

But the ties that bind them could also become their friendship's Kryptonite.

Both have been known to be fiercely loyal to their families -- and big boosters of each of their parent's presidential bids.

\"I can tell you, there is no better person than my father to have in your corner when you're facing tough opponents or making hard decisions,\" Ivanka said when introducing her father as he formally announced his candidacy for president. \"He is battle-tested.\"

How big a role each of them play on the campaign trail is still unclear.

But both Ivanka and Chelsea are seen as having real potential to help boost the image -- to humanize and soften -- each of their parents.

That's something polls show both Hillary Clinton and Donald Trump struggle with as candidates.